Non-volatile memory devices are widely used in many consumer, commercial and other applications. While some non-volatile memory devices, such as flash memory, use accumulated charge to store data, some other memory devices, such as resistive random access memory (RRAM), phase change RAM (PRAM), and magnetic RAM (MRAM), use change in resistivity of a material therein to store data.
A resistive memory cell generally includes a first electrode, a second electrode, and a variable resistivity material connected therebetween. The resistive memory cell can be configured so that the resistivity of the material is controlled in response to a voltage that is applied between the first and second electrodes.
A PRAM device may include a phase changeable material layer which functions as a variable resistivity material. In response to sufficient heat, the phase changeable material layer may change phase so that its resistance changes and remains changed after its temperature returns to a pre-heating level. The phase changeable material layer may be formed from a chalcogenide material that includes germanium (Ge), antimony (Sb), and/or tellurium (Te) (“GST”). The phase of the material can be controlled in response to a level of current and/or duration of current that is applied to an electrode to heat the material a sufficient amount to change its phase.
The resistance of the phase changeable material layer varies in response to its phase changes. For example, when the phase changeable material has crystalline characteristics, its resistance can be substantially less than when the phase changeable material layer has amorphous characteristics. Accordingly, the resistance of the phase changeable material in a PRAM device is controlled to store a logic value and is sensed to read the logic value.